Square wave generator



Aug. 4, 1942.

BLISS S QUARE WAVE GENERATOR Filed so, '1940 Wig/ABLE FULL WAVEFREQUENCY 0.5C/LLATOR REfT/F/ER PHASE .SH/FTER FZ/u. WAVE RECTIFIER 2Sheets-Sheet 1 our ur GAS'DISCHARG 15 755 UTILIZATION ems/um: DEV/CEOSCIHATOR f0 OUTPUT FROM /8 "RECTIFIER I6 I N VEN TOR.

WARREN H. BLISS A TTORNEY.

Aug. 4, 1942.

INPUT W. H. BLISS SQUARE WAVE GENERATOR Filed Aug. 50, 1940 sets-Sheet 2INVENTOR. 1 EN H. BLISS Patented Aug. 4, 1942 UNITED STATES PATENTOFFICE SQUARE WAVE GENERATOR Warren H. Bliss, Maplewood, N. 1., assignorto Radio Corporation of America, New York, N. Y., a corporation ofDelaware Application August 30, 1940, Serial No. 354,830

6 Claims.

This invention relates to an improvement in generators for producingcurrent or voltage variations of substantially square or rectangularwave form.

Frequently it is desirable to generate current or voltage variations ofsquare or rectangular wave form of a predetermined frequency and it isalso often desirable that the ratio of the positive to the negativehalf-cycles of the generated wave form be differentially adjustable.Wave forms of such shape are particularly useful in facsimiletransmitting systems where a system using constant frequency variabledot transmission is employed. Furthermore, voltage variations of squareor rectangular wave form are frequently desirable in televisiontransmission, and in fact voltage or current variations of such waveform may be used in many respects where it is desired that the voltageof the wave form be cyclically increased to a predetermined valuesubstantially instantaneously and remain at that value for apredetermined length of time.

A new and improved square or rectangular wave generator has thereforebeen developed which is simple and positive in operation and whichemploys a minimum amount of electrical apparatus. Furthermore, thegenerator as developed and as described herein is capable of producingoscillations of square or rectangular wave form of substantially anydesired frequency, and it is also capable of regulation whereby theratio of the positive and negative half cycles of the wave form may bedifferentially varied.

It is, therefore, one purpose of the present invention to provide a newand improved square or rectangular wave form generator by means of whichcurrent or voltage variations of square or rectangular wave form may begenerated.

It is still another purpose of the present invention to provide a squareor rectangular wave form generator in which definite control may beexercised over the ratio between the lengths of the'positive and thenegative half-cycles of the wave forin generated.

Still another purpose of the present invention resides in the provisionon. square or rectangular wave form generator in which the frequency ofthe wave form generated may be readily controlled.

Other advantages and purposes of the present invention will become moreapparent to those skilled in the art from a reading of the followingspecification and claims, particularly when considered with thedrawings, wherein like reference Figure 1 shows the elements of thepresent invention schematically in block diagram,

Figure 2 shows curves of potential variatifns which appear at the outputterminals of varparticular desired frequency. The particular frequencyoscillator used is not vital, and may be an ordinary source of 60-cyclepower supply where low frequency waves are desired, or the oscillatormay take the form of a well-known Hartley or Colpitts oscillator. Sincethe present invention is not concerned primarily with the particularoscillator used, the oscillator is not shown in detail. It is desirable,however, that the voltage variations of the oscillations produced by theoscillator vary substantially as a sine function or some closely similarvoltage variation. The oscillations which are supplied by the frequencyoscillator ID are fed to a phase shift device l2 which, through manualcontrol, is capable of shifting the phase relationship of the voltagevariation preferably from about zero to the oscillator.

The oscillations as derived directly from the frequency oscillator l0and as also derived from the phase shifter l2, are supplied to twoindependent full-wave rectifiers l4 and It for supplying uni-directionalpulsating current. The rectifiers do not include any filtering circuitsfor reasons which will be explained later. The outputs from thefull-wave rectiflers are therefore pulsating uni-directional voltagevariations of identical frequency and substantially identical wave form,the phase relationship of the pulsations being determined by the degreeof phase shift introduced *bythe phase shifter l2. These pulsations fromthe full-wave -rectiflers H and it are then supplied to a gas dischargesquarenr rectangular wave generator l8 from which oscillations of thedesired wave form are derived.

characters reprwent like parts and wherein: 'The phase shifter I 2 isshown in detail in Figure 3 and at the input terminals 22 and 24 areimpressed the oscillations as produced by the oscillator l8. Theseoscillations are induced in the secondary winding of the transformer 26and across the secondary winding is placed a load resistance orimpedance 28 in order that some loading will be present on thetransformer. Also connected across the secondary of the transformer 26is a series arrangement of a condenser 38 and resistance 32. In parallelwith these elements is a second series arrangement of a resistance 34and condenser 38. These resistances and condensers are connected asindicated in the figure, and the two resistances 32 and :34 arepreferably of the same value and are preferably so arranged as to besimultaneously adjustable in value. The condensers 30 and 36 are alsopreferably of the same value, and may or may not be so arranged as to besimultaneously controlled as to their value.

An electron discharge tube 38 is also used which includes a cathode, acontrol electrode and an anode. The cathode of the discharge tube 38 isconnected to ground or to the negative terminal of a source of anodepotential by means of a resistance 48 which is by-passed by condenser42. The control electrode or grid of the tube 38 is connected to thejunction of the series-connected condenser 30 and resistance 32 whilethe junction point of the resistance 34 and condenser 36 is connected toground. By reason of these connections there appears between the controlelectrode and the cathode of tube 38 a voltage variation of the samefrequency as the impressed voltage variation, but the phase relationshipof the potential applied between the control clectrade and the cathodewith respect to the input voltage variation depends upon the value ofthe resistances 32 and 84. The tube 38 operates primarily as anamplifier tube, since the adjustable phase alteration in the appliedvoltage variation is a result of the resistance-condenser combinations38-32 and 34-38. By varying the value of the resistances 32 and 3dsimultaneously, and

by equal amounts, the phase relationship of the voltage impressed uponthe control electrode of the tube 38 with respect to the voltagevariations impressed upon the terminals 22 and 28 may be varied fromsubstantially zero to 980 degrees. The voltage variations which areimpressed upon the control electrode and the cathode of tube 38 are,therefore, present in the anode circuit of the tube 38 and by means ofthe transformer 88 these voltage variations are caused to appear at theoutput terminals 48, 48 and 58 which are connected to the secondary ofthe transformer 44.

As stated above, the voltage variations as supplied directly by theoscillator i8 and by the phase shifter I2 are of the same identicalfrequency, but are displaced in phase relationship and these voltagevariations are each separately rectified by full-wave rectifiers l4 andI8 respectively. Since the operation of the present invention does notdepend upon the specific rectifier used, no particular details of thiselement are shown, since any conventional and practical fullwaverectifier may be used. Normally it would be desirable to use a rectifiersimilar to that used for supplying anode current to the tubes in a radioreceiving set or a simple duo-diode: tube may be utilized to afford thedesired rectification. The rectifier includes only the rectifier tube orthe asymmetric unit which performs the function of rectifying thevoltage variations, and no filter circuit is used so that the outputfrom the rectifiers is somewhat cycloidal in wave form and amounts to apulsating direct current or potential. Since the square or rectangularwave form generator (to be hereinafter described in detail) responds tochanges in the potential or the pulsating wave form derived from therectifiers, in order that the square wave generator may remain as stableas possible it is desired that the generator respond to the voltagevariation at a. point where its rate of change is substantially thegreatest. Since this is the case, the output from the rectifier ispreferably derived from the negative terminal of the rectifier whichwould be the terminal 48 of the output transformer 44 shown in Figure 3if a conventional electronic rectifier is used.

The wave forms of the various potential variations appearing in thesystem are shown in Figure 2, the wave form 5| representing the voltagevariations as derived directly from the frequency oscillator l8.Associated with this wave form is shown a second wave form 52 ofidentical frequency, the wave form 52 being displaced in phaserelationship with respect to the wave form 5!. This displacement, whichis a result of the operation of the phase shifting device shown inFigure 3, is indicated by Figure 2 as being of the order ofapproximately degrees. The voltage variation represented at 5| issupplied to the full-wave rectifier l4, and the output from thisrectifier is indicated by the curve or wave form 53 which, of course,includes pulsations of a frequency double the frequency of the impressedwave form 5|. The wave form shown at54 is the result of the full-waverectification of the wave form shown at 52, and bears a phaserelationship with respect to the pulsating wave form shown at 53 asdetermined by the phase relationship of the wave forms impressed on therectifiers, The pulsating wave forms shown at 53 and 58 are impressedupon the square or rectangular wave form generator, and in response tothese wave forms current or voltage variations of square or rectangularwave form is generated.

The elements of the square wave generator are shown specifically inFigure l, and include gas discharge tubes 58 and 62. These gas dischargetubes may be of any type, but are preferably of the type generally knownby the name thyra. tron. The gas discharge tubes each include a cathode,a control electrode and an anode. The cathode of the gas discharge tube68 is connected to ground by way of resistance 6|, which is bypassed bycondenser 84 and the anode of the tube 68 is connected to the positiveterminal of a source of potential through a load resistance 68. Thecontrol electrode for the gas discharge tube 60 is connected to theinput terminal 68 by way of a resistance 10 and -a source of biasingpotential 12, and the terminal 68 is connected to ground through a gridresistance H. The potential variations as derived from the full-waverectifier l4 are impressed upon the terminal 88 and accordingly controlthe potential of the control electrode of tube 88 with respect to itsassociated cathode.

The gas discharge tube 62 is also connected to ground by way of cathoderesistor 16 which is bypassed by condenser 18, and the anode of the tube62 is connected to the positive terminal of a source of potential by wayof the load resistance 88. The control electrode of the gas dischargetube 62 is connected to input terminal 82 by way of the resistance 84and the grid bias potential 86. A control electrode resistance 88 isalso connected between the input terminal 82 and ground.

In order that the gas discharge tubes II and 62 may be made to operatealternately, their anodes are connected together by means of condenser90 so that a change in the potential at one anode will accordinglyaffect the potential impressed upon the anode of the other tube.Therefore, if one of the gas tubes is conducting at any particularinstant, and the control electrode oi the other gas tube is madesufllciently positive to permit a discharge through that tube, then thepresence of current in the second tube, by reason of the condenser ll,will cause a cessation of current flow in the first tube, assuming, ofcourse, that the control electrode of the first tube is at a potentialbelow that required to initiate a discharge in that tube. Thyratrons,"being gas discharge tubes, are responsive to the potential of thecontrol electrode in that the control electrode may initiate a dischargein the tube, but after a discharge has been initiated the controlelectrode loses control and the discharge will be maintained until theanode potential is removed or reduced below a value capable ofmaintaining a sustained discharge. The amount of current which flowsthrough the discharge tube is limited by the impedance of the tube plusthe impedance of the cathode and anode load resistances.

Since the pulsating voltage variations shown at 53 and 54 in Figure 2,as derived from the fullwave rectifiers l4 and it, are impressed uponthe terminals 68 and B2 of the circuit shown in Figure 4, the operationof the gas discharge tubes 60 and 62 will depend upon the occurrence andpresence of these impulses at the terminals 68 and 82. Each time apositive impulse is applied to the control electrode of one of the gasdischarge tubes, that particular tube will become conducting, and theother tube will be made nonconducting. This is by reason of theinclusion of the condenser 90 as explained above, and furthermore, thecontrol electrodes of the gas discharge tubes 50 and 62 are biasednegative with respect to their associated cathodes by an amountdetermined by the size of the potential sources 12 and 86. Thesepotential sources are so adjusted and their values are so chosen thatthe control electrodes are negative with respect to their associatedcathodes by an amount suflicient to require the pulsations representedat 53 and 54 to be of the order indicated by the dotted line shown onthese curves. Accordingly, gas discharge tube 60 will become conductingonly when the pulsating potential shown at the curve 53 increases to avalue equal to or greater than that represented by the dotted line shownassociated with the curve, and similarly, gas discharge tube 62 is madeconducting only when the potential applied to its control electrode isof the order of that indicated by the dotted line associated with thecurve 54.

In explaining the operation of the square or rectangular generator, itwill be assumed that gas discharge tube 60 is conducting, and that tube62 is in a non-conducting condition. A positive impulse applied to theterminal 82 and to the control electrode of the discharge tube 62 will.cause the tube 62 to become conducting and by reason of the condenser90. the tube 60 will simultaneously be rendered non-conductive since inthe meantime the potential of the control electrode of tube 60 has beenreduced to a value below that which will initiate a discharge in tube60. Tube 62 will then continue to conduct current until tube 60 is againrendered conductive as a result of a positive impulse being applied toterminal 68. This alternate operation of the gas discharge tubes 60 and62 continues so long as alternate positive impulses are applied to theirrespective control electrode terminals, and the circuits associated withthe gas discharge tubes 60 and 62 are so arranged that the tubes willnot, of their own accord, oscillate as a relaxing generator in theabsence of positive driving impulses.

During the time that the one or the other of the two gas discharge tubesare in a conducting condition, there is, of course, a certain amount ofcathodic current present in the cathode resistor of that tube. Thepresence of this current will produce a certain voltage drop across thecathode resistor, and this voltage drop will have a value dependent uponthe intensity of the current flowing through the resistor. Furthermore,in the absence of current in the cathode resistor, there will be nopotential drop thereacross, and no voltage will appear at the outputterminals of the square wave form generator. The output wave form may bederived from across either of the two cathode resistors 6| or 18, sincethese two resistors carry current alternately and the only differencebetween the wave form which is developed across the one resistance orthe other lies in the fact that they are of opposite polarity. As statedabove, however, either cathode resistor may be used as the element fromwhich the desired wave form is derived.

The wave form of the voltage variation appearing across resistance SI oftube 60 is indicated at 55 in Figure 2, and the wave form of the voltagevariation appearing across the resistance 16 of tube 62 is indicated at56 in Figure 2. Since, in Figure 2, the phase displacement of thevoltage variation 52 is displaced approximately degrees with respect tothe voltage variation shown at 5|, then the positive and negative halfcycles of the waves shown at 55 and 55 will be substantially equal. If.however, it is desired that the positive or negative half cycle ofeither of the waves shown at 55 or 56 be increased or decreased, it isonly necessary to alter the phase displacement of the wave form which issupplied to the rectifier [6 which is accomplished through asimultaneous adjustment of the resistors 32 and 34 of the phase shifter.Since the phase shifter is capable of introducing a change in the phaserelationship of from substantially zero to substantially degrees, thenthe positive or negative half cycle of the produced wave form may bedecreased to substantially zero or'may be increased to occupysubstantially the entire cycle of the wave alternation.

The intensity of the produced voltage variation of square or rectangularwave form depends upon the intensity of the current passed by the gasdischarge tubes 60 and 62, and upon th size of their cathode resistors.If this voltage variation is insufficient for the Purposes for whichthey are generated, they may be intensified by applying themto anamplifier 20 as indicated in Figure 1. Such amplification is, undercertain circumstances, unnecessary.

The frequency of the generated wave form may be controlled by alteringthe frequency of the generated wave form as produced by the frequencyoscillator ill. The adjustment of this oscillator depends upon the typeoscillator used, and since oscillators in which the frequency may becontrolled are well known in the art, no specific oscillator is shown.

From the above it may be seen that a new and improved system has beendevised for producing oscillations of square or rectangular wave form,and furthermore it will be seen that the system as devised is simple inoperation and includes a small number of components. Furthermore, inview of the use of gas discharge tubes which offer very low impedance tothe flow of current therethrough, the amount of current passed by thetube is limited primarily by the resistances connected in circuittherewith, and since these resistances remain fixed in value, theamplitude of the wave form generated remains substantially constant.Furthermore, since gas discharge tubes are used which build up theirmaximum current output substantially instantaneously, the change fromthe positive to the negative half cycle of the generated square wave issubstantially instantaneous.

It is to be understood that although a more or less specific form ofphase shifter is shown and described in this application, it is notnecessary that such phase shifter be used since various other phaseshifters could as well be substituted for the one shown.

Various other alterations and modifications may be made in the presentinvention .without departing from the spirit and scope thereof, and

it is desired that any and all such modifications be considered withinthe purview of the present invention except as limited by thehereinafter appended claims.

I claim:

1. A generator for producing voltage variations of substantiallyrectangular wave form comprising a pair of gas discharge tubes each ofwhich includes a cathode, a control electrode and an anode, meansincluding a resistance for connecting each cathode to a point of fixedpotential, a condenser connected between the anodes, and means formaintaining each of the control electrodes negative with respect to itsassociated cathode by an amount suilicient to prevent initiation of adischarge through the tubes, means ior impressing upon the controlelectrodes phase displaced positive impulses of identical frequencywhereby the discharge tubes will be caused to be rendered alternatelyconductive whereby potential variations of substantially rectangularwaveform may be produced across the cathode resistances of eachdischarge tube, and means for varying the phase relationship of thepositive impulses which are applied to the control electrodes of thetubes.

2. A device for producing potential variations of substantiallyrectangular Wave form comprising means for generating an oscillation ofsubstantially sine wave form and of a predetermined frequency, means forshifting the phase of the produced oscillation, means for rectifying theoscillations produced directly by said first named means and theoscillations from the phase shifting means whereby two series of impulseof identical frequency and of displaced phase relation ship may beproduced, a pair of gas discharge tubes each including a cathode, acontrol electrode and an anode, means including a resistance formaintaining each anode positive with respect to its cathode, a condenserconnected between the anodes of such tubes, and means for individuallyimpressing the two series of impulses upon the control electrodes ofsaid tubes whereby 75 potential variations of substantially rectangularwave form may be produced by said tubes.

3. A device for producing potential variations of substantiallyrectangular wave form comprising means for generating an oscillation ofsubstantially sine wave form and of a predetermined frequency,controllable means for shifting the phase of the produced oscillation apredetermined amount, means for rectifying the oscillations produceddirectly by said first named means, means for rectifying theoscillations from the phase shifting means, whereby two series ofimpulses of identical frequency and of variable phase relationship maybe produced, a pair of gas discharge tubes each including a cathode, acontrol electrode and an anode, means including a resistance formaintaining each anode positive with respect to its cathode, means formaintaining each control electrode negative with respect to its cathode,a condenser connected between the anodes of such tubes, and means forimpressing the two series of impulses upon the control electrodes ofsaid tubes individually whereby potential variations of substantiallyrectangular wave form may be produced by each 01 said tubes.

4. A device for producing potential variations of substantiallyrectangular wave form comprising an oscillation generator for producingan oscillation of substantially sine wave form and of a predeterminedfrequency, adjustable means for shifting the phase of the producedoscillation, means for rectifying the oscillations produced directly bythe oscillation generator and th oscillations from the phase shiftingmeans whereby two series of positive impulses of identical frequency andof variable phase relationship may be produced, a pair of gas dischargetubes each including a cathode, a control electrod and an anode, meansincluding a resistance for maintaining each anode positive with respectto its cathode, a reactance device connected between the anodes of suchtubes, and means for impressing the two series of positive impulses tothe control electrodes of said tubes individually whereby potentialvariations of substantially rectangular wave form may be produced bysaid tubes.

5. A device for producing voltage variations of substantiallyrectangular wave form comprising a pair of gas discharge tubes eachincluding a cathode, a control electrode and an anode, a source ofpotential having a positive and negative terminal, a resistanceconnected between the positive terminal of the source of potential andeach of the anodes, a resistance connected between the negative terminalof the source of potential and each of the cathodes, a condenserconnected between th anodes of each of the tubes, means for maintainingeach of the c0ntrol electrodes negative with respect to their associatedcathodes by an amount sulficient to prevent an electron flow through thetubes, means for individually impressin upon the control electrodes aseries of positive impulse 01 identical frequency but displaced in"phase relationship, and means for varying the phase displacement of theimpulses whereby the tubes may be rendered alternately conducting andwhereby the tubes may be caused to produce voltage variations ofsubstantially rectangular wave form.

6. A device for producing voltage variations of substantiallyrectangular wave form comprising a pair of gas discharge tubes eachincluding a cathode, a control electrode and an anode, a

source of potential having a positive and negative terminal, animpedance connected between the positive terminal of the source ofpotential and each of the anodes, an impedance connected between thenegative terminal 01 the source of potential and each 01' the cathodes,a reactance connected between the anodes of each of the tubes, means fornormally maintaining each of the control electrodes negative withrespect to the cathode associated therewith by an amount suflicient toprevent the initiation or an electron flow through the tubes, means forindividually impressing upon the control electrodes a separate series ofpositive impulses of identical frequency but of displaced phaserelationship whereb the tubes may be rendered alternately conducting toproduce a voltage variation of substantially rectangulanwave form, andmeans for varying the phase displacement of the impulses of one of theseries of impulses with respect to th im- 1 pulses of the other of theseries of impulses.

WARREN H. BLISS.

